System and method for recompletion of old wells

ABSTRACT

A system for recompletion of an old well in order to achieve an increased oil recovery from a reservoir, said system comprising a pipe inserted into the old well, at least two constrictors or swell packers being arranged along the length of the recompleted well and defining a well section between two successive constrictors or swell packers, said system further comprising at least one autonomous valve arranged in said well section defined between said two successive swell packers or constrictors. Disclosed is also a method for recompletion of an old well in order to achieve an increased oil recovery from a reservoir.

The present invention relates to a system and method for recompletion of old wells. More specifically the invention relates to a system and a method as disclosed in the preamble of claim 1 and 7, respectively.

In a preferred embodiment of the invention a plurality of autonomous valves or flow control devices are substantially as those described in WO 2008/0048745 A1, belonging to the applicant of the present application.

Devices for recovering of oil and gas from long, horizontal and vertical wells are known from US patent publications Nos. 4,821,801, 4,858,691, 4,577,691 and GB patent publication No. 2169018. These known devices comprise a perforated drainage pipe with, for example, a filter for control of sand around the pipe. A considerable disadvantage with the known devices for oil/and or gas production in highly permeable geological formations is that the pressure in the drainage pipe increases exponentially in the upstream direction as a result of the flow friction in the pipe. Because the differential pressure between the reservoir and the drainage pipe will decrease upstream as a result, the quantity of oil and/or gas flowing from the reservoir into the drainage pipe will decrease correspondingly. The total oil and/or gas produced by this means will therefore be low. With thin oil zones and highly permeable geological formations, there is further a high risk that of coning, i.e. flow of unwanted water or gas into the drainage pipe downstream, where the velocity of the oil flow from the reservoir to the pipe is the greatest.

From World Oil, vol. 212, N. 11 (11/91), pages 73-80, is previously known to divide a drainage pipe into sections with one or more inflow restriction devices such as sliding sleeves or throttling devices. However, this reference is mainly dealing with the use of inflow control to limit the inflow rate for up hole zones and thereby avoid or reduce coning of water and or gas.

WO-A-9208875 describes a horizontal production pipe comprising a plurality of production sections connected by mixing chambers having a larger internal diameter than the production sections. The production sections comprise an external slotted liner which can be considered as performing a filtering action. However, the sequence of sections, of different diameter creates flow turbulence and prevent the running of work-over tools.

U.S. Pat. No. 5,435,393 describes a production pipe with a lover drainage pipe divided into sections and with one or more inflow restriction devices which controls the flow of oil or gas from the reservoir into the drainage pipe based on the precalculated loss of friction pressure along the drainage pipe, the precalculated production profile of the reservoir and the precalculated inflow of gas or water. This publication does thus not relate to recompletion of old wells, nor to the use of autonomous flow control devices in said recompletion.

When extracting oil and or gas from geological production formations, fluids of different qualities, i.e. oil, gas, water (and sand) is produced in different amounts and mixtures depending on the property or quality of the formation. None of the above-mentioned, known devices are able to distinguish between and control the inflow of oil, gas or water on the basis of their relative composition and/or quality.

With the autonomous valve as described in WO 2008/0048745 A1 is provided an inflow control device which is self adjusting or autonomous and can easily be fitted in the wall of a production pipe and which therefore provide for the use of work-over tools. The device is designed to “distinguish” between the oil and/or gas and/or water and is able to control the flow or inflow of oil or gas, depending on which of these fluids such flow control is required.

The device as disclosed in WO 2008/0048745 A1 is robust, can withstand large forces and high temperatures, needs no energy supply, can withstand sand production, is reliable, but is still simple and very cheap.

A problem with the prior art is that the well, with or without inflow control devices, has to be abandoned since the well is not able to produce anymore due to gas and/or water breakthrough.

In existing wells large quantities of oil will remain along the path of the well due to “short-circuit” effects, i.e. that only parts of the well are producing oil. As shown in the enclosed FIG. 9 a section of the well path adjoins a high permeability zone in which substantially all the inflow occurs. In such high permeability zones gas and/or water will enter at a faster rate than in other zones of the well. If gas experiences a break-through in such high permeability zones the gas will flow even easier than the oil (gas has a higher mobility than oil) such that this zone will increase its proportion of the total inflow compared with a situation in which oil was present there. If water experiences a breakthrough, water will also flow easier that oil. The importance of this will be increasing with a higher difference in viscosity between oil and water. These effects reduce the drainage rate.

Short-circuit effects might also appear in low oil zones with zones comprising gas and/or water above or below them.

The system and method according to the invention seeks to reduce or eliminate the above and other problems or disadvantages by inserting a pipe with a at least one, and preferably a plurality of autonomous valves into an existing well, and thus increase oil recovery with limited investments. The invention might thus be regarded as an improvement of an existing stinger solution in which an impervious pipe section having solid walls are arranged on a location in the well in which gas breakthrough previously has been experienced.

The system and method according to the invention are characterized by the features as disclosed in the characterizing clause of claim 1 and 7, respectively.

Advantageous embodiments are set forth in the dependent claims.

The present invention will be further described in the following by means of examples and with reference to the drawings, where:

FIG. 1 shows a schematic view of a production pipe with a control device according to WO 2008/0048745 A1,

FIG. 2 a) shows, in larger scale, a cross section of the control device according to WO 2008/0048745 A1, b) shows the same device in a top view.

FIG. 3 is a diagram showing the flow volume through a control device according to the invention vs. the differential pressure in comparison with a fixed inflow device,

FIG. 4 shows the device shown in FIG. 2, but with the indication of different pressure zones influencing the design of the device for different applications.

FIG. 5 shows a principal sketch of another embodiment of the control device according to WO 2008/0048745 A1,

FIG. 6 shows a principal sketch of a third embodiment of the control device according to WO 2008/0048745 A1,

FIG. 7 shows a principal sketch of a fourth embodiment of the control device according to WO 2008/0048745 A1.

FIG. 8 shows a principal sketch of a fifth embodiment of WO 2008/0048745 A1 where the control device is an integral part of a flow arrangement.

FIG. 9 shows a principal view of a prior art well intersecting a high permeability zone of a reservoir.

FIG. 10 shows a principal view of the well in FIG. 9, which, in accordance with the invention, is recompleted with a new pipe with autonomous valves inserted into the well, causing a substantially uniform inflow into the well.

FIG. 11 a shows a principal view of a lateral well in accordance with the invention, e.g. the well in FIG. 10, and

FIG. 11 b shows an enlarged principal view of the part of FIG. 11 a constricted by a circle.

FIG. 1 shows, as stated above, a section of a production pipe 1 in which a control device 2, according to WO 2008/0048745 A1 is provided. The control device 2 is preferably of circular, relatively flat shape and may be provided with external threads 3 (see FIG. 2) to be screwed into a circular hole with corresponding internal threads in the pipe or an injector. By controlling the thickness, the device 2, may be adapted to the thickness of the pipe or injector and fit within its outer and inner periphery.

FIG. 2 a) and b) shows the prior control device 2 of WO 2008/0048745 A1 in larger scale. The device consists of a first disc-shaped housing body 4 with an outer cylindrical segment 5 and inner cylindrical segment 6 and with a central hole or aperture 10, and a second disc-shaped holder body 7 with an outer cylindrical segment 8, as well as a preferably flat disc or freely movable body 9 provided in an open space 14 formed between the first 4 and second 7 disc-shaped housing and holder bodies. The body 9 may for particular applications and adjustments depart from the flat shape and have a partly conical or semicircular shape (for instance towards the aperture 10.) As can be seen from the figure, the cylindrical segment 8 of the second disc-shaped holder body 7 fits within and protrudes in the opposite direction of the outer cylindrical segment 5 of the first disc-shaped housing body 4 thereby forming a flow path as shown by the arrows 11, where the fluid enters the control device through the central hole or aperture (inlet) 10 and flows towards and radially along the disc 9 before flowing through the annular opening 12 formed between the cylindrical segments 8 and 6 and further out through the annular opening 13 formed between the cylindrical segments 8 and 5. The two disc-shaped housing and holder bodies 4, 7 are attached to one another by a screw connection, welding or other means (not further shown in the figures) at a connection area 15 as shown in FIG. 2 b).

The present invention exploits the effect of Bernoulli teaching that the sum of static pressure, dynamic pressure and friction is constant along a flow line:

$p_{static} + {\frac{1}{2}\rho \; v^{2}} + {\Delta \; p_{friction}}$

When subjecting the disc 9 to a fluid flow, which is the case with the present invention, the pressure difference over the disc 9 can be expressed as follows:

${\Delta \; p_{over}} = {\left\lbrack {p_{{over}{(P_{4})}} - p_{{under}({f{({p_{1},p_{2},p_{3}})}}}} \right\rbrack = {\frac{1}{2}\rho \; v^{2}}}$

Due to lower viscosity, a fluid such as gas will “make the turn later” and follow further along the disc towards its outer end (indicated by reference number 14). This makes a higher stagnation pressure in the area 16 at the end of the disc 9, which in turn makes a higher pressure over the disc. And the disc 9, which is freely movable within the space between the disc-shaped bodies 4, 7, will move downwards and thereby narrow the flow path between the disc 9 and inner cylindrical segment 6. Thus, the disc 9 moves dawn-wards or up-wards depending on the viscosity of the fluid flowing through, whereby this principle can be used to control (close/open) the flow of fluid through of the device.

Further, the pressure drop through a traditional inflow control device (ICD) with fixed geometry will be proportional to the dynamic pressure:

${\Delta \; p} = {{K \cdot \frac{1}{2}}\rho \; v^{2}}$

where the constant, K is mainly a function of the geometry and less dependent on the Reynolds number. In the control device according to the present invention the flow area will decrease when the differential pressure increases, such that the volume flow through the control device will not, or nearly not, increase when the pressure drop increases. A comparison between a control device according to the present invention with movable disc and a control device with fixed flow-through opening is shown in FIG. 3, and as can be seen from the figure, the flow-through volume for the present invention is constant above a given differential pressure.

This represents a major advantage with the present invention as it can be used to ensure the same volume flowing through each section for the entire horizontal well, which is not possible with fixed inflow control devices.

When producing oil and gas the control device according to the invention may have two different applications: Using it as inflow control device to reduce inflow of water, or using it to reduce inflow of gas at gas break through situations. When designing the control device according to the invention for the different application such as water or gas, as mentioned above, the different areas and pressure zones, as shown in FIG. 4, will have impact on the efficiency and flow though properties of the device. Referring to FIG. 4, the different area/pressure zones may be divided into:

-   -   A₁, P₁ is the inflow area and pressure respectively. The force         (P₁·A₁) generated by this pressure will strive to open the         control device (move the disc or body 9 upwards).     -   A₂, P₂ is the area and pressure in the zone where the velocity         will be largest and hence to represents a dynamic pressure         source. The resulting force of the dynamic pressure will strive         to close the control device (move the disc or body 9 downwards         as the flow velocity increases).     -   A₃, P₃ is the area and pressure at the outlet. This should be         the same as the well pressure (inlet pressure).     -   A₄, P₄ is the area and pressure (stagnation pressure) behind the         movable disc or body 9. The stagnation pressure, at position 16         (FIG. 2), creates the pressure and the force behind the body.         This will strive to close the control device (move the body         downwards).

Fluids with different viscosities will provide different forces in each zone depending on the design of these zones. In order to optimize the efficiency and flow through properties of the control device, the design of the areas will be different for different applications, e.g. gas/oil or oil/water flow. Hence, for each application the areas needs to be carefully balanced and optimally designed taking into account the properties and physical conditions (viscosity, temperature, pressure etc.) for each design situation.

FIG. 5 shows a principal sketch of another embodiment of the control device according to WO 2008/0048745 A1, which is of a more simple design than the version shown in FIG. 2. The control device 2 consists, as with the version shown in FIG. 2, of a first disc-shaped housing body 4 with an outer cylindrical segment 5 and with a central hole or aperture 10, and a second disc-shaped holder body 17 attached to the segment 5 of the housing body 4, as well as a preferably flat disc 9 provided in an open space 14 formed between the first and second disc-shaped housing and holder bodies 4, 17. However, since the second disc-shaped holder body 17 is inwardly open (through a hole or holes 23, etc.) and is now only holding the disc in place, and since the cylindrical segment 5 is shorter with a different flow path than what is shown in FIG. 2, there is no build up of stagnation pressure (P₄) on the back side of the disc 9 as explained above in conjunction with FIG. 4. With this solution without stagnation pressure the building thickness for the device is lower and may withstand a larger amount of particles contained in the fluid.

FIG. 6 shows a third embodiment according to WO 2008/0048745 A1 where the design is the same as with the example shown in FIG. 2, but where a spring element 18, in the form of a spiral or other suitable spring device, is provided on either side of the disc and connects the disc with the holder 7, 22, recess 21 or housing 4.

The spring element 18 is used to balance and control the inflow area between the disc 9 and the inlet 10, or rather the surrounding edge or seat 19 of the inlet 10. Thus, depending on the spring constant and thereby the spring force, the opening between the disc 9 and edge 19 will be larger or smaller, and with a suitable selected spring constant, depending on the inflow and pressure conditions at the selected place where the control device is provided, constant mass flow through the device may be obtained.

FIG. 7 shows a fourth embodiment according to WO 2008/0048745 A1, where the design is the same as with the example in FIG. 6 above, but where the disc 9 is, on the side facing the inlet opening 10, provided with a thermally responsive device such as bi-metallic element 20.

When producing oil and/or gas the conditions may rapidly change from a situation where only or mostly oil is produced to a situation where only or mostly gas is produced (gas breakthrough or gas coning). With for instance a pressure drop of 16 bar from 100 bar the temperature drop would correspond to approximately 20° C. By providing the disc 9 with a thermally responsive element such as a bi-metallic element as shown in FIG. 7, the disc will bend upwards or be moved upwards by the element 20 abutting the holder shaped body 7 and thereby narrowing the opening between the disc and the inlet 10 or fully closing said inlet.

The above examples of a control device as shown in FIGS. 1 and 2 and 4-7 are all related to solutions where the control device as such is a separate unit or device to be provided in conjunction with a fluid flow situation or arrangement such as the wall of a production pipe in connection with the production of oil and gas. However, the control device may, as shown in FIG. 8, be an integral part of the fluid flow arrangement, whereby the movable body 9 may be provided in a recess 21 facing the outlet of an aperture or hole 10 of for instance a wall of a pipe 1 as shown in FIG. 1 instead of being provided in a separate housing body 4. Further, the movable body 9 may be held in place in the recess by means of a holder device such as inwardly protruding spikes, a circular ring 22 or the like being connected to the outer opening of the recess by means of screwing, welding or the like.

FIG. 9 shows a principal view of a well 24 intersecting a high permeability zone 25 of a reservoir 26. As indicated by the size of the arrows the inflow into the well 24 is non-uniform, and with a breakthrough in the zone 25 in which substantially all of the inflow occurs.

FIG. 10 shows a principal view of the well in FIG. 9, which, in accordance with the invention, is recompleted with a new pipe 27 with autonomous valves (not shown in this figure) inserted into the well, causing a substantially uniform inflow into the well. A plurality of constrictors or swell packers 29 are arranged along the well to seal between the inserted pipe 27 and the existing well 24.

FIGS. 11 a and 11 b respectively show a principal view of a lateral well in accordance with the invention, e.g. the well shown in FIG. 10, and an enlarged principal view of the part of FIG. 11 a constricted by a circle. In FIG. 11 b the existing or old well 24 is indicated by dotted lines and the new pipe 27 with autonomous valves 2 (of which only one is shown for clarity) is indicated by solid lines. Preferably a plurality of autonomous valves 2 are arranged along the length of the inserted pipe 27, and preferably at least one valve 2 in each pipe section defined between two successive constrictors or swell packers 29, in order to create a substantially uniform inflow into the recompleted well 24, 27 and thus an increased oil recovery.

An embodiment of a method according to the invention preferably comprises the following steps (not necessarily in said order):

-   -   Providing an old well 24,     -   Providing a new pipe 27 comprising a plurality of autonomous         valves 2 arranged along the length of the pipe 27,     -   passing said pipe 27 into said old well 24 for recompleting the         old well 24,     -   providing a plurality of swell packers or constrictors 29 along         the well to seal between the inserted pipe 27 and the old well         24 and to define a plurality of well sections between two         successive constrictors or swell packers 29 in each of which         sections at least one autonomous valve 2 is to be located,     -   in order to create a substantially uniform inflow into the         recompleted well 24, 27 and thus an increased oil recovery.

Further, the inserted pipe 27 preferably covers substantially the whole length of the old well 24.

In a most basic embodiment according to the invention, the pipe 27 just covers a limited length to be arranged at a very distinct location in the well 24 in which breakthrough is to be prevented, i.e. a distinct fraction in the formation or reservoir 26 intersected by the well 24. This location will then be isolated by providing one constrictor or swell packer 29 on each side of said fraction, and with just one autonomous valve 2 arranged in such a single isolated section of the well.

With the valve or control device described in WO 2008/0048745 A1, due to the constant volume rate, a much better drainage of the reservoir is thus achieved. This result in significant larger production of that reservoir.

Even though the well 24 shown in FIGS. 9-11 is a horizontal or lateral well, it should be emphasized that wells of any inclination, including vertical wells, are within the scope of the present invention as stated in the appended claims.

As also mentioned in the introductionary part of the description, the autonomous valves 2 preferably are those described in WO 2008/0048745 A1 and above, but any type of autonomous valve (e.g. electronically operated) is conceivable within the context of the invention. 

1. A system for recompletion of an old well in order to achieve an increased oil recovery from a reservoir, said system comprising: a pipe inserted into the old well, at least two constrictors or swell packers being arranged along the length of the recompleted well and defining a well section between two successive constrictors or swell packers; and at least one autonomous valve arranged in said well section defined between said two successive swell packers or constrictors.
 2. A system according to claim 1, wherein a plurality of well sections are defined along the length of the well and that at least one autonomous valve is arranged within each well section.
 3. The system according to claim 1, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure.
 4. The system according to claim 1, wherein the inserted pipe covers substantially the whole length of the old well.
 5. The system according to claim 1, wherein the well is a horizontal well.
 6. The system according to claim 1, wherein the well is a well of any inclination from horizontal, including vertical.
 7. A method for completion of an old well in order to achieve an increased oil recovery from a reservoir, comprising the following steps (not necessarily in said order): providing a pipe comprising at least one autonomous valve arranged in the pipe, passing the pipe into the old well for recompleting said old well, providing at least two swell packers or constrictors along the well to seal between the inserted pipe and the old well to define at least one well section between said two successive constrictors or swell packers in which at least one well section the at least one autonomous valve is arranged.
 8. A method according to claim 7, further comprising the step of providing a plurality of well sections along the well in each of which sections at least one autonomous valve is arranged.
 9. The method according to claim 8, further comprising the step of covering substantially the whole length of the old well with the inserted pipe.
 10. The method according to claim 7, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure.
 11. The system according to claim 2, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure.
 12. The system according to claim 2, wherein the inserted pipe covers substantially the whole length of the old well.
 13. The system according to claim 3, wherein the inserted pipe covers substantially the whole length of the old well.
 14. The system according to claim 2, wherein the well is a horizontal well.
 15. The system according to claim 3, wherein the well is a horizontal well.
 16. The system according to claim 4, wherein the well is a horizontal well.
 17. The system according to claim 2, wherein the well is a well of any inclination from horizontal, including vertical.
 18. The system according to claim 3, wherein the well is a well of any inclination from horizontal, including vertical.
 19. The system according to claim 4, wherein the well is a well of any inclination from horizontal, including vertical.
 20. The method according to claim 8, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure. 